Herbicides used on turfgrasses generally fall into two categories:
1. Preemergence herbicides, which must be applied prior to the germination of monocotyledon annual weed grass seeds, such as crabgrass, annual bluegrass (poa annua), etc., most commonly are mytotic root inhibitors. These inhibitors prevent emergence and growth of the weed grass shoot by preventing the root from developing as it emerges from the seed. These herbicides are active in the soil where their presence in the soil or at the soil surface prior to seed germination is essential for efficacious herbicidal performance. Accordingly, these herbicides commonly are applied as a granular product, such as small 1.0-1.5 mm clay granules or 2.0 mm-2.5 mm fertilizer granules which have 1% to 2% of the herbicide active ingredient absorbed or coated onto the granule surfaces. These granules, when distributed, penetrate through the turfgrass foliage to the soil surface where the herbicide desorbs from the granule into the soil solution. Preemergence herbicides commonly used are in a family of dinitroaniline chemicals, such as benefin, trifluralin, and oryzalin. This category of products are generally described in U.S. Pat. Nos. 3,705,794; 3,798,276; 4,063,929 and 4,025,329 which describe products having varying particle sizes.
2. Postemergence herbicides are applied to weed foliage after emergence from dicotyledon seeds, commonly referred to as broadleaf weeds, such as dandelion, plantain, white clover, henbit, spurge, etc. These are systemic auxinic herbicides which require foliar absorption and subsequent translocation within the weed plant for efficacious weed kill. These herbicides commonly are mixed in water or liquid fertilizers and applied as liquid sprays. Liquid droplet size in the spray is controlled by pressure and orifice size. Droplet sizes of about 500 to 2000 microns generally are acceptable. Air currents present during application can cause undesired drift of droplets, which-are too small (less than 200 microns), onto foliage and kill susceptible, desired plants such as ornamental and vegetable plants. Liquid-sprayed postemergence auxinic herbicides commonly used in turfgrass applications are phenoxy and benzoic chemicals, such as 2,4-dichlorophenoxy-acetic acid (2,4-D), 4-chloro-2-methylphenoxy acetic acid (MCPA), 2-(4-chloro-2-methyl phenoxy) propanoic acid (mecoprop), and 3,6-dichloro-2-methylbenzoic acid (dicamba).
Combination postemergence herbicide-blended granular fertilizer products, often referred to as "Weed and Feed" (W&F) products, were developed for weed control and fertilization in residential lawns. They are used by the do-it-yourself homeowner and lawn service companies to save time and money with the dual value product--herbicide plus fertilizer--in one application. Blended turfgrass fertilizers, customarily comprised of regular-sized granular basic fertilizer materials, nominal size, 2.5 mm, are sourced from among such regular-sized materials as urea, coated urea, ammonium sulfate, ammoniated phosphate, potassium chloride or sulfate, and non-nutrient filler granules such as sized limestone granules. These regular-sized blended fertilizers were reformulated as W&F products by replacing the heavy fillers with lightweight particles of the same compatible regular size, such as ground corn cob and granulated peanut shells. These light particles then are referred to as lightweight carriers for the herbicides. This entire blend of regular-sized heavy granular fertilizer materials and lightweight granular carriers is impregnated or coated with the postemergence herbicides by the W&F manufacturer.
When the W&F is spread by the homeowner onto the weedy lawn turfgrass, it is a labeled direction for use to either water the turfgrass first or apply the W&F when the turfgrass is wet with dew. This is required to provide the adhesion of the fertilizer and carrier particles to any prostrate or upright weed foliage with which they come into contact during the spreading application. However, despite the moistened weed foliage, most of the regular size, heavy fertilizer granules, rather than adhere to, rebound from the weed foliage to the soil below. While some of the lightweight carrier particles in the blend do adhere effectively to the weed foliage, their presence in the W&F product generally is less than 30% of the total granules so there is low contact frequency with the population of weed foliage present in the turfgrass area to which the regular-sized W&F is applied.
Further, at the nominal 2.5 mm size of regular blended fertilizers/carriers used in residential W&F products, which generally are in a distribution of granule particle sizes from 1.5 mm to 3.0 mm (1500 to 3000 microns), the number of regular-sized particles spread or distributed onto the turfgrass typically is in the range of 150 to 300 total particles per square foot. However, only about 10% to 25% of the total number of those particles are the lightweight carrier particles. Consequently, the distribution of particles, which reasonably might contact and adhere to the weed foliage, is only in the range of 15 to 75 particles per square foot, or about from one carrier particle per 10 square inches to one carrier particle per 2 square inches of turfgrass area.
Consequently, the weed control afforded by these regular-sized granular blended fertilizers and lightweight carriers impregnated with postemergence herbicides repeatedly has been significantly inferior to that of liquid spray-applied postemergence herbicides. In these granule vs. liquid herbicide comparisons identical herbicides are compared at the same applied rates, usually expressed as weight of herbicide active ingredient per unit area, such as per acre. The liquid herbicide-treated area for the comparison is separately prefertilized with a granular fertilizer at the same nutrient treatment rate as that of the regular-sized granular W&F treatment.
Generally, weed control ratings of these two applications, depending on the applied herbicide rate, at four to five weeks after treatment are:
% Weed Control Treatment Range Typical 1. Liquid spray herbicide and 85-100 90 separately applied granular fertilization. 2. Weed and Feed granular, blended herbicide-fertilizer combination product. Regular size (2.5 mm) 10-60 30
Accordingly, there is a need for a granular weed & feed product which has weed control approaching the weed control of a liquid spray herbicide. The present invention relating to postemergence herbicides applied as weed & feed granules, meets that need.